Sunderland have made attempts to sign striker Steven Fletcher from Wolves but so far without success, and O'Neill appears determined to add to his attack before the close of the transfer window.

Speaking to the Sunderland Echo, O'Neill said: "You might tell me the lack of goals highlights it, and it may well do, but throughout we've been saying we need to strengthen.

"It would have been nice to have had a full complement of players and everything sorted out so they got to know each other's play, but the strengthening of the side is obvious to everyone."

So far, Sunderland have only been able to add former Aston Villa defender Carlos Cuellar to their ranks, but O'Neill remains optimistic he can bring new faces to the Stadium Of Light.

"Pre-season is over now," O'Neill added. "A lot of our guys go away on international duty which is a concern, but the other boys that we have at home, we'll work with them this week and between now and transfer deadline day, we'll try to improve the quality of the squad.

"Obviously things will develop and happen, but I can't be sure of the date."